Method of drying pasted-plate storage battery electrodes



United States Patent 3,227,584 METHOD OF DRYING PASTED-PLATE STORAGE BATTERY ELECTRODES Paul Arnold, Hannover, Germany, assignor to Varta Aktiengesellschaft, Hagen, Westphalia, Germany, a corporation of Germany No Drawing. Filed June 29, 1961, Ser. No. 149,796

4 Claims. (Cl. 136-33) The present invention relates to a method for drying pasted storage battery plates, particularly for lead-acid batteries, without causing cracks in the plates.

Various methods for curing pasted plates have been proposed. It has been suggested, for instance, to dry the pasted plates first in tunnel ovens or a flash drier and then to permitthe partially dried plates to remain stored for two to five days. Such plates are dry and properly oxidized but they show cracks. It has also been proposed to pre-dry positive pasted plates and immediately thereafter to subject them at higher temperatures to a humid atmosphere. Allegedly, the drying time in this procedure is only 45 minutes but it is not possible to avoid storing the dried plates before formation for at least about 36 hours so that the desired chemical reactionsof the active mass may be largely completed and the plates may be properly dried. While the latter procedure has certain advantages, it does not preclude the formation of cracks in the plates.

All known cun'ng methods for pasted plates, which avoid the formation of cracks, take at least about 21 hours or more. Such methods require a great amount of space and are not adapted for the continuous production of electrodes.

It is the primary object of the present invention to provide a method for drying or curing pasted plates without causing cracks in the plates in a substantially shorter period of time than possible with conventional curing procedures whereby the continuous manufacture of plates is facilitated.

The above and other objects are accomplished in accordance with this invention by drying the surfaces of the pasted plates in several stages at different temperatures, preferably first rising from stage to stage and then decreasing, cooling the thus superficially dried plates in an air stream, subjecting the cooled plates to a humid atmosphere, and finally completing the drying in warm air.

In accordance with a preferred embodiment, the surfaces of the pasted-plate electrodes are dried in a first stage at a temperature between about 70 C. and about 80 C., in a second stage at a temperature of about 200 C., and in a third stage at a temperature of about 100 C., the total drying time in the three stages being quite short and being of the order of about one half to one and a half minutes when the electrodes are rather Widely spaced. The preferred spacing of the electrodes during the surface drying is in the range of 80 mm. to 120 mm., about 100 mm. having been found most satisfactory. A maximiim drying time of about 50 seconds in each stage sufiices.

After this surface drying, the pasted-plate electrodes are not yet free of moisture and the exothermic reaction of the active mass in the electrodes would cause cracks therein. This is avoided according to the invention by cooling the superficially dried pasted plates. While the plates are subjected to a cooling stream of air, their spacing is considerably reduced, preferably to a range of 2 mm. Of course, cooling may also be effected by merely blowing cool air over each electrode or in any other suitable manner.

After the pasted-plate storage battery electrodes have been cooled substantially to room temperature, they are subject to a humid atmosphere. Preferably, they are first humidified for about four hours, a range of about 3 hours 3,227,584 Patented Jan. 4, 1966 "ice to about 5 hours being acceptable, for instance, by placing them on racks and putting moist sheets thereover or spraying the plates with water, whereupon they may be subjected to a water vapor spray at a preferred temperature of about C. A water vapor spray treatment of about one hour will sufiice to produce substantial oxidation of the lead in the active mass.

Final drying is accomplished in warm air, the preferred method being subjecting the pasted plates to a temperature of about 80 C. for about half an hour and then completing the drying at a temperature of about 200 C. for about one hour, for instance, by positioning the plates over an open flame. The final drying temperatures may vary between about C. and about 210 C. and the total final drying time may be in relation to the chosen drying temperature about 2 hours, either in a single stage or in the indicated, preferred two stages, the period of each stage being suitably adjusted to obtain the desired degree of curing.

While the present invention is not concerned with any particular paste composition and is applicable to all pasted plates for storage batteries, particularly electrodes for lead-acid batteries, it will be illustrated by way of example in connection with the commonly used pastes prepared by mixing some particular lead oxide, such as litharge, red lead, or uncalcined, high-metallic oxides, or a blend of such oxides with a dilute solution of sulfuric acid. This mixture results in reactions leading to the formation of basic lead sulfate and the liberation of considerable heat. After the reaction temperature has passed its maximum, the paste is applied to the electrode grids when it has the consistency of a fairly stiff mortar. The exact formulation of the paste is a matter for the individual manufacturer and forms no part of the present invention. Normally, the leady component of the dry mix will be about 99% and this mix is blended with sulfuric acid to produce the paste.

After the paste is applied to the grid it must be cured before formation, which is accomplished in the drying process of the present invention. It has been found that during the initial surface drying of the plates, the moisture of the paste is reduced not very much. The subsequent cooling and the following treatment in a humid atmosphere reduces the moisture in the plates to about 8% by weight of the plates. The moisture is finally reduced to between about 2.5% and about 1.5%, by Weight, in the final drying step.

Following is a specific example to illustrate the drying process of the invention.

Example A paste consisting of 1000 g. lead dust with a content of 71% by weight of PhD and g. sulfuric acid with 5.6. 1.09 was prepared and applied to grids of a lead alloy with 7% of antimony, said grids having a size of 14.3 cm. x 12.4 cm., about 135 g. of paste being used per grid. The moisture content of the paste applied to the grids was about 14%, by weight of the paste. The pasted plates were stacked at a distance of 100 mm. from each other and rapidly moved through a three-stage drying oven at successive temperatures at 75 C., 200 C., and 100 0., remaining at each stage for about 30 seconds. After this surface drying treatment, the moisture content of the paste had been reduced to about 13.6%, by weight. The plates were now moved together to a distance of about 2 mm. and subjected to a cooling air blast for about 9 min. until they had assumed room temperature. Subsequently, wet sheets were placed over the stacked plates and the plates remained covered with the Wet sheets for four hours, their moisture content decreasing to about 12.5%, by weight of the paste. After this, they were subjected to a water vapor spray at a temperature of 80 C. for an hour to assist in the oxidation of metallic lead in the paste.

Finally, the pasted plates were subjected to warm air at a temperature of 80 C. for half an hour and placed over an open flame in an atmosphere of 200 C. temperature for an hour to complete the drying and to obtain a final moisture content of 2.1% by weight of the paste. The plates were now ready for formation.

With the drying process of the present invention, dry plates without cracks may be produced in a period of about six to seven hours, which is about one third of the time previously required for readying plates for the formation process. Also, the process is adapted to continuous manufacturing operations without the need for excessive space. An additional advantage of the present drying process consists in the fact that a thin oxide skin is formed on the electrodes in the very first minutes of curing, which is stabilized in the immediately following cooling step and is not cracked during the subsequent curing steps. This oxidized skin is first present only on the surfaces of the plates while the active mass Within the pastes is not yet fully oxidized. The metallic lead in the interior of the active mass of the plate is oxidized only when the plates are subjected to a humid atmosphere at an elevated temperature.

The curing process of the present invention is applicable to all conventional positive and negative pasted plates for storage batteries, requires no complicated apparatus or skilled labor, and produces in a substantially reduced time superior pasted plates without cracks, which may be readily formed and have a considerably increased life.

While the invention has been described in connection with certain preferred embodiments thereof, it will be readily understood that many modifications and variations may occur to those skilled in the art, particularly after benefitting from the present teaching, without departing from the spirit and scope of this invention as defined in the appended claims.

I claim:

1. A method of drying pasted-plate storage battery electrodes, comprising the steps of drying the surfaces of the pasted-plate electrodes in three successive stages, each lasting a maximum of about 50 seconds and the temper ature in the first stage being between about 70 C. and about 80 C., in the second stage about 200 C., and in 4 the third stage about 100 C.; subjecting the superficial- 1y dried electrodes to a cooling stream of air to cool the electrodes to about room temperature; subsequently subjecting the cooled electrodes to a humid atmosphere; and finally completing the drying in warm air at a temperature in the range of about 80 C. up to about 210 C.

2. The method of claim I, wherein the electrodes are spaced more closely during cooling than during the surface drying stages.

3. The method of claim 1, wherein the final drying is effected in two stages at a respective temperature of about 80 C. and about 200 C.

4. A method of drying pasted-plate storage battery electrodes, comprising the steps of drying the surfaces of the pasted-plate electrodes in three successive stages, each lasting about 30 seconds and the temperature in the first stage being about C., in the second stage about 200 C., and in the third stage about 100 C.; subjecting the superficially dried electrodes to a cooling air blast for about nine minutes until they have assumed room temperature; subsequently covering the cooled electrodes with wet sheets for about four hours; subjecting the humidified electrodes to a water vapor spray having a temperature of about C. for about an hour; then subjecting the electrodes to hot air for about 80 C. temperature for about half an hour; and completing the drying by subjecting the electrodes to a temperature of about 200 C. for an hour.

References Cited by the Examiner UNITED STATES PATENTS 2,130,246 9/1938 Olcott et a1 34-12 2,300,628 11/1943 Merson 34-150 2,553,192 5/1951 Hindall 136-33 2,656,399 10/1953 Hindall 136-33 2,656,400 10/1953 Carson 136-33 2,686,213 8/1954 Smyth 136-34 OTHER REFERENCES Vinal: Storage Batteries, 4th Edition, 1955, page 36.

WINSTON A. DOUGLAS, Primary Examiner.

NORMAN YUDKOFF, MURRAY TILLMAN, JOHN H. MACK, Examiners. 

1. A METHOD OF DRYING PASTED-PLATE STORAGE BATTERY ELECTRODES, COMPRISING THE STEPS OF DRYING THE SURFACES OF THE PASTED-PLATE ELECTRODES IN THREE SUCCESSIVE STAGES, EACH LASTING A MAXIMUM OF ABOUT 50 SECONDS AND THE TEMPERATURE IN THE FIRST STAGE BEING BETWEEN ABOUT 70*C. AND ABOUT 80* C., IN THE SECOND STAGE ABOUT 200*C., AND IN THE THIRD STAGE ABOUT 100*C.; SUBJECTING THE SUPERFICIALLY DRIED ELECTRODES TO A COOLING STREAM OF AIR TO COOL THE ELECTRODES TO ABOUT ROOM TEMPERATURE; SUBSEQUENTLY SUBJECTING THE COOLED ELECTRODES TO A HUMID ATMOSPHERE; AND FINALLY COMPLETING THE DRYING IN WARM AIR AT A TEMPERATURE IN THE RANGE OF ABOUT 80*C. UP TO ABOUT 210*C. 